1. Field of the Invention
This invention relates to roofing products, or sheet-type roll roofing, used to seal substrate structures and the process for making the same. More particularly, the present invention is in the field of roofing underlayments commonly used in residential and commercial applications.
2. Description of Prior Art
Underlayment materials are widely used in roofing applications. They are commonly used under asphaltic shingles, shakes, slate, cedar, tile, and metal panels in addition to being used in build-up roofing (BUR) and modified bituminous roofing applications. The primary objective of using an underlayment in residential application is to provide a secondary water barrier on the roof. Underlayment is also used as a barrier on the deck when applying roofing membranes by various application methods such as torching or hot mopping. These are also used in applications of self-adhering membranes when the building codes prohibit direct adhesion to wood substrates. Underlayments are typically fastened to the roof deck using roofing nails or staples.
These products have continued to evolve over the years. In the early part of the 20th century, asbestos fiber based roofing felts were used; however these are not used anymore due to health hazards associated with asbestos. For several decades, underlayment products have been manufactured using organic felts. These materials are commonly referred to as No. 15 and No. 30 felts. These are manufactured by coating organic felt (a. k. a. paper) with asphalt, and are relatively inexpensive materials.
However felts have several limitations. They have poor tensile strength, which causes felt to tear easily resulting from foot traffic during the installation process. Once installed, felts also tear easily due to wind. When exposed to the elements, felts experience thermal expansion and contraction, which leads to wrinkles and fishmouths. Moreover, when left exposed, they deteriorate with time. Availability of felt fluctuates greatly, especially when the demand increases dramatically after weather-related events such as hurricanes. Also the price of felt is greatly dependent upon crude oil price. These uncertainties, coupled with the disadvantages of felt, have led to the development of alternate materials.
In early 2000s, synthetic underlayments were introduced in the market. These non-asphaltic materials are based on plastics such as polyethylene and polypropylene. Most synthetic underlayments are manufactured by laminating two or more layers of polymeric films or fabrics. These products have gained popularity due to several inherent advantages over felt. Some of the main benefits: lightweight, more coverage per roll, lays flat, wrinkle-free, excellent tensile and tear strength, superior resistance to UV light, resistance to algae, fungi and mold, resistance to rot and decay, etc. Though higher priced than felts, synthetic underlayments have been gaining market share due to their advantages over felt.
However synthetics do have several disadvantages. For one, they have no long term proven performance as roofing underlayments. Almost all synthetic underlayments are laminants of two or more polymeric sheets that are thermally or chemically bonded together. Since they are laminates, there is a strong possibility of delamination of the component layers when exposed to the elements after installation. Also, most synthetics do wrinkle when exposed to sunlight. Another disadvantage is that these products do not seal around fasteners; therefore only certain types of fasteners are permitted to be used with synthetic underlayments. Most synthetics have poor traction, i. e., these sheets are slippery at higher slopes, particularly under wet conditions.
Another type of underlayments used is generally referred to as ‘base sheets’; these are widely used in commercial roofing applications. Base sheets are polyester or fiberglass reinforced materials that are saturated and coated with an asphaltic material or modified asphaltic material, and surfaced with parting agents such as sand, talc or fine mineral aggregate. The modified asphaltic material could be an atactic polypropylene (APP) or Styrene-Butadiene-Styrene (SBS) based formulation.